1. Field of the Invention
The present invention relates to a fin slitting machine and method. More specifically, the present invention relates to a method and apparatus for maintaining co-acting slitter wheels in registration to enable a sheet of fin stock to be slit prior to being formed into a fin configuration for a heat exchanger.
2. Description of the Prior Art
In a wound fin type heat exchanger wherein a metallic fin is wound helically about a tube to promote heat transfer there are many types of fin configurations which may be utilized. Typically, a solid, smooth surface tube has a projecting fin member extending therefrom to promote heat transfer from fluid flowing through the tube to air or another gas flowing in heat exchange relation with the tube and fin mounted on the exterior surface thereof.
The fin configuration may be one of many known shapes. One of the preferred configurations is to form a fin into a U-shape having a solid center portion which is wound abutting the exterior surface of the tube to promote heat transfer therebetween and having the two leg portions of the U separated from the adjacent leg portions and extending outwardly therefrom. These leg portions form a myriad of tiny spines which upon the fin being wrapped about a tube separate to form a random series of projections defining a heat exchange surface.
This U-shaped fin is formed by slitting a roll of fin stock such that the fin stock mantains a solid center portion and has spaced slits extending outwardly therefrom to the outer edge of the fin stock on both sides. This flat fin stock is then rolled into a U-shaped configuration with the solid center portion forming the base of the U and the slit side portions extending to form the legs thereof. This then U-shaped fin stock is wound about the tube to form the heat exchanger.
Co-acting slitter wheels slit the fin stock to provide the outwardly extending slits from the solid center portion. The slitter wheels each have a series of teeth projecting therefrom which co-act to displace the material in the fin sheet forming the slit therebetween. This slitting is done at relatively high speeds and it is necessary to maintain the slitter teeth in registration with each other as both slitter wheels are rotated at sufficient speed.
The prior art discloses a co-acting slitter wheels mounted such that one is driven in a first direction by a motor. A gear on the shaft of the first slitter wheel interacts with a gear on the shaft of the second slitter wheel to drive the second slitter wheel in the opposite direction. To prevent backlash between the slitter wheels and to maintain the teeth of the slitter wheels in registration, a second motor is applied to the shaft of the second slitter wheel in a direction opposite the direction of rotation of the second slitter wheel to maintain a force thereon. This counteracting force maintains the gears in engagement and allows the slitter teeth to be maintained in registration. Another method similar to that described is the use of a friction brake to maintain a force on the second slitter wheel.
It is necessary to provide a positive means of maintaining registration since the speed of the slitter wheels may be varied in conjunction with the speed that the fin is being wound onto a tube. Hence, the motor driving the first slitter wheel will vary in rotational speed and consequently the second slitter must likewise vary. Without a positive means of maintaining the second slitter wheel in registration it might overrun or underrun the first slitter wheel as the speed of rotation is changed.
It is necessary to maintain the slitter teeth in registration since, should the spacing between the slitter teeth become too large, the slit will not be formed. Should the spacing between the teeth become too small, damage to the slitter wheels may occur.
The present invention incorporates a notched pulley mounted on the shaft of each slitter wheel. A double sided belt having projections co-acting with the notches of each pulley is wound therebetween to rotate the pulleys in opposite directions. The double sided belt acts to maintain the pulleys in registration and allows a small amount of flexibility therebetween to prevent damage to the slitter wheels while maintaining the slitter teeth in the appropriate position.